Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 05 2023 08:16:50 FOUS30 KWBC 050816 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 415 AM EDT Mon Jun 05 2023 Day 1 Valid 12Z Mon Jun 05 2023 - 12Z Tue Jun 06 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... ....Southern Plains through the Northern Rockies... Not a lot of changes made to the previous Excessive Rainfall Outlook for this time period as the persistent, stagnant blocked flow persists across the nation. There will continue to be an axis of above average PW stretching from the Southern to Central High Plains, through the Central to Northern Rockies and into the Northern High Plains. Embedded in this high PW axis will be numerous vorts that will help enhance uvvs and convective activity. The last several days, areas of the Southern High Plains from northeast NM into the TX/OK Panhandle have seen some organization and locally heavy totals than other areas that have not seen as much overlap. For this reason, we continue to depict a slight risk area from northeast NM into Northwest TX where models again show potential for additional convection. There is a typical amount of model qpf spread but at least some consensus in the models for additional convection across areas that are more hydrologically sensitive given recent rains. The slight risk area fits well with where the latest HREF neighborhood probabilities are high for 1"+ rains and overlap with the above mentioned heavy rains over the past few days. HREF probabilities are also high for 1"+ amounts in spots through the marginal risk area, but do not have the consistent overlap with recent heavy rain areas of previous days as do sections of the Southern High Plains. ....Central California coast Range into the Sierra Nevada... A strong closed low offshore of Southern California will be swinging steadily northeastward to a position at the coast Monday afternoon at which time it is then expected to slow significantly. An increasingly upper difluent flow pattern to the north and northeast of this closed low will support increasing scattered convection Monday afternoon from the central California Coast Range, northeastward into the Sierra in a region where PW values will be rising to 1 to 2+ standard deviations above the mean.=20=20=20 The previous marginal risk area was expanded to the southwest from the Sierra to the Central California Coast Range where the latest HREF probabilities show some potential for hourly rainfall rates of .50-1" in this anomalous PW axis from Monday afternoon into evening. With stream flows remaining above average, isolated flash flooding possible. In addition, some of this heavy rain potential may occur across burn scar regions from the past several years. ....Upper Midwest... A marginal risk was maintained along and ahead of the strengthening frontal boundary forecast to stretch northwest to southeast from south central Canada into eastern portions of the Northern Plains and Upper MS Valley. With PW rising to 2+ standard deviations above the mean in an axis of MUCAPE values 1000-2000 J/kg in the vicinity of this front, locally heavy rainfall amounts are possible. The simulated radars from the latest CAM guidance suggests potential for slow moving cells in the vicinity of this front. With areas of higher than average stream flow as per the National Water Model from south central MN northwestward along the MN/ND border, isolated runoff issues possible from hourly rainfall rates of 1"+ with these slower moving cells. The marginal risk area agrees well with the latest CSU first guess fields which shows a marginal risk across eastern ND into northwestern MN. Oravec Day 2 Valid 12Z Tue Jun 06 2023 - 12Z Wed Jun 07 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... ....Southern High Plains through the Northern Rockies... The stagnant, blocked mid to upper level pattern across large portions of the nation day 1 will persist into the day 2 period.=20 This will keep the Excessive Rainfall Outlook very similar to the day 1 outlook, especially through the Southern to Central High Plains, Central to Northern Rockies into portions of the Northern High Plains. There will once again be an axis of above average PW values with embedded mid to upper level vorts/enhanced upper difluence across these areas. This will support another day of widespread scattered convection with locally heavy rainfall amounts. There continues to be some model signal for organized heavy rains over portions of the Southern High Plains that have seen areas of heavy rains over the past several days. This will continue to support a slight risk area where higher stream flow and soil moisture will increase the risk of additional flash flooding. ....Portions of the Northern Plains... A surface frontal boundary expected to remain stationary day 2 in the vicinity of eastern ND and western MN. An axis of anomalous PW values 2.5"+ standard deviations above the mean and 1000-1500 j/kg MUCAPE in the vicinity of this front will support additional locally heavy rainfall amounts. With stream flows remaining high along the ND/MN border area and potential for some overlap of day 1 heavy rains with day 2 heavy rains, a marginal risk area was added from the previous for this period. This again agrees well with the latest CSU first guess field for the day 2 period which show a small marginal risk along the ND/MN border area. ....Central California coast/Northern Sierra/Northern California into portions of the Great Basin... The strong closed mid to upper low along the Southern CA coast at the end of day 1 will move only slowly inland day 2. This will maintain a very upper difluent pattern to the north and northeast of the closed low from the Central CA coast, northeast through the northern Sierra/northern CA and into the Great Basin. Similar to the day 1 period, the previous marginal risk area was drawn farther to the southwest to the central CA coast region where models are showing some convective potential on the north side of the closed low closer to the central CA coast in a continued axis of much above average PW values, 2+ standard deviations above the mean. Widespread scattered convection also likely farther northeastward across the northern Sierra/northern CA into portions of the Great Basin in the above mentioned region of well defined upper difluence. Similar to the day 1 period, with stream flows remaining above average across the marginal risk area, isolated flash flooding is possible and also a risk for burn scar areas from the past few years. Oravec Day 3 Valid 12Z Wed Jun 07 2023 - 12Z Thu Jun 08 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... ....Southern High Plains through the Northern Rockies... With little forecast change to the large scale blocking pattern across the nation, the Excessive Rainfall Outlook will be very similar to the day 2 outlook. Widespread scattered convection is again likely stretching from the Southern to Central High Plains, northward through the Central to Northern Rockies into the Northern High Plains in what will continue to be an axis of above average PW values. There is a model signal for increasing PW anomalies day 3 over the Central to Northern Rockies region where upper difluence also strengthens day 3 ahead of the upstream closed low moving slowly from Southern CA into the Great Basin.=20 There is an increase in model consensus precip across the Central to Northern Rockies which may eventually lead to a greater risk area denoted, but for the time being, the risk is maintained at marginal. Farther to the south, a slight risk was introduced for the same general region of the Southern High Plains as for the day 1 and 2 periods. Although there is again the typical amount of model qpf detail spread for a day 3 forecast, there continues to be a model signal for another round of potentially heavy rains to affect portions of the Southern High Plains from northeast NM into the TX/OK Panhandle/northwest TX region. Given the recent pattern of daily heavy rains, a slight risk is warranted for the potential for additional day 3 rains across the Southern High Plains. ....Northern Sierra/Northern California into portions of the Great Basin... The strong closed low over Southern CA day 2 will continue to move only slowly northeast into the Great Basin day 3. This will again maintain a very upper difluent pattern to its northeast across the northern Sierra, northern CA into the Great Basin. Maintained a marginal risk area across these regions for isolated flash flooding in the persistent axis of much above average PW values, 1 to 2+ standard deviations above the mean. ....Coastal Southeast Florida... Added a marginal risk area for the urban corridor along the Southeast Florida from Miami north to approximately Vero Beach.=20 There is an uptick in model qpf day 3 compared to day 2 as shortwave energy pushes east northeastward from eastern Gulf across South Florida. Enhanced upper difluence forecast to push across South Florida where PW values rise to 1.75-2". With models showing potential for heavy rains, can not rule out isolated urban runoff issues. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6n0hm71kfe_LVlAeMEcFiiRCR1upA1aYffthgzreKPkG= L53sPI758sAlGooMHTe_77Luro-WA1_Klh9QFLwlDSaENGM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6n0hm71kfe_LVlAeMEcFiiRCR1upA1aYffthgzreKPkG= L53sPI758sAlGooMHTe_77Luro-WA1_Klh9QFLwl4Kk1mrE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6n0hm71kfe_LVlAeMEcFiiRCR1upA1aYffthgzreKPkG= L53sPI758sAlGooMHTe_77Luro-WA1_Klh9QFLwllZqc_4U$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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